1. Field of the Disclosure
The present subject matter generally relates to oil level sight windows for gearboxes.
2. Description of Related Art
Engine-driven mechanisms require a minimum amount of a lubricant to ensure proper operation of the moving parts of the drive system. In some engine-driven mechanisms, such as agricultural equipment, the drive system includes a gearbox containing various gears, shafts, and other moving parts, as well as an amount of oil for lubricating the moving parts.
An exemplary prior art gearbox 10 is illustrated in FIG. 1. The gearbox 10 includes a gearbox housing 12 with opposing walls 14 and 16. A pair of bearing bores 18 and 20 are defined in the opposing walls 14 and 16, respectively. The bearing bores 18 and 20 are aligned with each other for mounting bearings (not illustrated) to support an input shaft (not illustrated) extending through the first bearing bore 18 and into the gearbox housing 12. A metallic bore cap plug 22 is associated with the second bearing bore 20 to isolate the interior of the gearbox housing 12 from the outside environment.
To fill the gearbox housing 12 with oil, a fill plug 24 on the top of the gearbox housing 12 is removed to expose a fill hole 26. Oil is poured into the gearbox housing 12 via the fill hole 26 and the fill plug 24 is replaced once the amount of oil in the gearbox housing 12 has reached the proper level. To ascertain the gearbox oil level, a side wall 28 of the gearbox housing 12 is provided with a small aperture 30 which receives a removable oil level plug 32. The level of oil in the gearbox housing 12 is checked by removing the oil level plug 32 and looking inside.
It has been recognized that removing an oil level plug to check the gearbox oil level can be disadvantageous, so in some gearboxes, the oil level plug is either replaced by or supplemented with a sight window. The sight window typically comprises the combination of an aperture in the gearbox housing and a lens received by or otherwise associated with the aperture. Rather than having to remove a plug to check the gearbox oil level, one merely looks through the sight window to verify the oil level.
One problem with a typical sight window is that it can be labor-intensive to retrofit onto a gearbox having only an oil level plug. For example, in some cases, a large aperture must be machined in a wall of the gearbox housing to receive a lens.
To simplify installation of a sight window in retrofitting situations, it is known to replace the standard (i.e., opaque) oil level plug with a plug having a built-in lens, such as the GN 743 line of oil level indicators from Elesa S.p.A. of Monza, Italy. Such oil level indicators avoid the problem of adding a large bore to the gearbox housing, but can be disadvantageous in that they are small, which can make it difficult to accurately assess the gearbox oil level.
Accordingly, there remains the need for a larger oil level sight window which can be easily retrofitted onto a gearbox having only an oil level plug.